Laser diode module

ABSTRACT

A laser diode module includes a laser diode emitting a laser beam, and a lens for collimating the laser beam. The lens is tilted with respect to an optical axis along which the laser beam is propagated.

This application is a continuation of application Ser. No. 08/088,647,filed Jul. 9, 1993, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to laser diode modules and, moreparticularly, to a laser diode module suitably applied to a bar codereader in which a laser diode is used as a light source.

2. Description of the Prior Art

Various types of laser sources have been proposed. In the past, a He--Nelaser was widely used. Recently, semiconductor laser diodes have beenproposed and applied to various fields as light sources. Suchsemiconductor laser diodes contribute to down-sizing of various devices.

A bar code reader that optically reads a bar code uses a semiconductorlaser diode (hereinafter, simply referred to as a laser diode).Normally, a laser diode is combined with optical elements such aslenses, and a laser diode module made up of the laser diode and theoptical elements is provided as a light source. A light emitted from thelaser diode is optically processed by the optical elements of the laserdiode module and is projected onto a bar code via an optical scanningsystem outside of the laser diode module.

The performance of the bar code reader greatly depends on theperformance of the laser diode module. Conventionally, a complexadjustment mechanism is employed in the laser diode module in order toimprove the performance thereof. For example, such an adjustmentmechanism is designed to adjust the positions of optical elements, suchas lenses. By way of another example, a plurality of optical elementsare used to improve the performance of the laser diode module.

From the above viewpoints, it is required to provide a simple laserdiode module capable of providing good performance by a simpleadjustment mechanism.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a simple laser diodemodule capable of providing good performance by a simple adjustmentmechanism.

The above object of the present invention is achieved by a laser diodemodule comprising: a laser diode emitting a laser beam; and a lens forcollimating the laser beam, the lens being tilted with respect to anoptical axis along which the laser beam is propagated.

It is preferable that the laser diode module comprises a base whichholds the laser diode; and a lens holder which holds the lens so that atilt angle of the lens with respect to the optical axis can be adjustedand which is mounted on the base.

It is also preferable that the laser diode module comprises a base whichholds the laser diode and has a mounting surface; a lens holder whichholds the lens and is slidably mounted on the mounting surface; and amechanism which tilts the lens holder with respect to the mountingsurface of the base so that the lens is tilted with respect to theoptical axis.

It is also preferable that the laser diode module comprises: a baseholding the laser diode and having a mounting surface; a first lensholder holding the lens; and a second holder slidably mounted on themounting surface of the base. The first lens holder has a first throughhole in which the lens is placed. The second holder has a second hole,into which the first lens holder is inserted, and two third holes joinedto the first through hole and formed on respective sides of the firstthrough hole. The laser beam emitted from the laser diode is propagatedthrough one of the two third holes, a part of the second hole, the lens,a remaining part of the second hole, and the other one of the two thirdholes.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of a bar code reader;

FIG. 2 is a diagram illustrating an astigmatic distance of a laser diodeand a positional deviation of the focal point due to such an astigmaticdistance;

FIG. 3 is a diagram of a conventional laser diode module;

FIG. 4 is a diagram explaining a phenomenon found by the inventors;

FIG. 5 is a graph of a relationship between a deviation of the positionof a beam waist and a lens tilting angle;

FIG. 6A is a front view of a laser diode module according to a firstembodiment of the present invention;

FIG. 6B is a side view of the laser diode module shown in FIG. 6A;

FIG. 6C is a perspective view of the laser diode module shown in FIGS.6A and 6B;

FIGS. 7A and 7B are diagrams illustrating variations in the position ofa screw hole formed in a lens holder used in the first embodiment of thepresent invention;

FIG. 8 is a front view of a variation of a base used in the firstembodiment of the present invention;

FIG. 9 is a front view of a laser diode module according to a secondembodiment of the present invention;

FIG. 10 is a perspective view of the laser diode module shown in FIG. 9;

FIG. 11A is a front view of a laser diode module according to a thirdembodiment of the present invention;

FIG. 11B is a side view of the laser diode module shown in FIG. 11A;

FIG. 11C is a perspective view of the laser diode module shown in FIGS.11A and 11B;

FIG. 12 is a side view of a first variation of a lens holder shown inFIGS. 11A through 11C;

FIG. 13 is a side view of a second variation of the lens holder shown inFIGS. 11A through 11C;

FIG. 14 is a side view of a third variation of the lens holder shown inFIGS. 11A through 11C;

FIG. 15A is a front view of a laser diode module according to a fourthembodiment of the present invention;

FIG. 15B is a side view of the laser diode module shown in FIG. 15A;

FIG. 15C is a perspective view of the laser diode module shown in FIGS.15A and 15B;

FIG. 16A is a front view of a laser diode module according to a fifthembodiment of the present invention;

FIG. 16B is a perspective view of the laser diode module shown in FIG.16A;

FIG. 17A is a front view of a laser diode module according to a sixthembodiment of the present invention;

FIG. 17B is a side view of the laser diode module shown in FIG. 17A;

FIG. 17C is a perspective view of the laser diode module shown in FIGS.17A and 17B;

FIG. 18A is a front view of a laser diode module according to a firstvariation of the laser diode module shown in FIGS. 17A through 17C;

FIG. 18B is a side view of the laser diode module shown in FIG. 18A;

FIG. 18C is a perspective view of the laser diode module shown in FIGS.18A and 18B;

FIG. 19A is a front view of a second variation of the laser diode moduleshown in FIGS. 17A through 17C;

FIG. 19B is a side view of the laser diode module shown in FIG. 19A;

FIG. 19C is a perspective view of the laser diode module shown in FIGS.19A and 19B;

FIG. 20A is a front view of a third variation of the laser diode moduleshown in FIGS. 17A through 17C;

FIG. 20B is a side view of the laser diode module shown in FIG. 20B; and

FIG. 20C is a perspective view of the laser diode module shown in FIGS.20A and 20B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to facilitate understanding of the present invention, adescription will now be given, with reference to FIG. 1, of a bar codereader.

Referring to FIG. 1, a bar code reader 1 is made up of a laser diodemodule 2 functioning as a light source, an optical scanning system 4, aphotodetector 9 and a processing circuit 10. A laser beam 3 emitted fromthe laser diode module 2 is oriented toward a good 6 and deflected asindicated by an arrow 5 by means of the optical scanning system 4, whichcomprises, for example, a polygon mirror and other mirrors. A bar code7, formed on the good 6, is scanned by the deflected laser beam 3. Thedeflected laser beam 3 is reflected by the bar code 7 and the intensitythereof is modulated (amplitude modulation). A reflected light 8 is thendetected by the photodetector 9, which outputs a corresponding electricsignal to the processing circuit 10. This circuit 10 performs apredetermined operation on the received electric signal, and generatesbar-code read data.

The laser diode module 2 includes a laser diode and an optical element.FIG. 2 shows an optical character of a laser diode of the laser diodemodule 2.

FIG. 2 shows a laser diode 11 used in the laser diode module 2. As shownin FIG. 2, the laser diode 11 has an astigmatic difference `a` normallyequal to 10 μm. In actuality, the astigmatic difference of normal laserdiodes ranges from 5 μm to 15 μm. Due to the astigmatic difference, afar-field pattern 13 of a laser beam 12 emitted from the laser diode 11is of an oval shape having a long axis 14 in the vertical direction anda short axis 15 in the horizontal direction.

When the laser beam 12 is focused by the lens 16, the focal point of alaser beam component 12_(V), in the vertical direction in a verticalplane, is defined as a vertical-direction focal point F_(V), and thefocal point of a laser beam component 12_(H), in the horizontaldirection in a horizontal plane, is defined as a horizontal-directionfocal point F_(H). When the aforementioned astigmatic difference rangeswithin ±5 μm, a distance `b` between the vertical-direction focal pointF_(V) and the horizontal-direction focal point F_(H) ranges within ± afew of tens of microns.

When different laser diodes have different distances `b`, different barcode readers have different read performances. With the above in mind,conventional laser diode modules are equipped with an adjustmentmechanism designed to make the difference `b` constant. Further, it isrequired to provide compact laser diode modules.

FIG. 3 shows a conventional laser diode module 20 made up of a laserdiode 22, a collimating lens 23, a cylindrical lens 24 and a cylindricallens 25, these elements being arranged on an optical axis Thecylindrical lens 24 functions to converge the laser beam emitted fromthe laser diode 22 in the vertical direction. The cylindrical lens 25functions to converge the laser beam in the horizontal direction. Thelenses 24 and 25 are provided so that the positions thereof areindependently adjusted along the optical axis 26. The position of thehorizontal-direction focal point F_(H) can be adjusted by adjusting theposition of the lens 25 along the optical axis 26. The position of thevertical-direction focal point F_(V) can be adjusted by adjusting theposition of the lens 24 along the optical axis 26.

However, the conventional laser diode shown in FIG. 3 has a disadvantagein that the module 20 is of a large size and is expensive due to use ofthe three lenses 23, 24 and

It is to be noted that the present invention is based on a phenomenonfound by the inventors. A description will now be given, with referenceto FIGS. 4 and 5, of such a phenomenon.

As shown in FIG. 4-(A) and FIG. 4-(B), the inventors attempted to tilt alens 30 with respect to a horizontal axis 31. At this time, theinventors observed that the position P_(H) of a beam waist of a beam32_(H) in the horizontal direction 32_(H) did not change, while theposition P_(V) of a beam waist of a beam 32_(V) in the verticaldirection 32_(V) changed from an original position P_(V) to a positionP_(V1) towards the lens 30.

The inventors also found that a tilt angle θ of the lens 30 and thedegree of positional variation in the beam waist P_(V) have arelationship indicated by a line I in FIG. 5. It can be seen from FIG. 5that the degree of positional variation in the beam waist P_(V) isincreased as the tilt angle θ is increased, within a certain range.

A description will now be given of embodiments of the present invention.It will be noted that the present invention has a mechanism for tiltinga lens.

FIGS. 6A, 6B and 6C are diagrams of a laser diode module 40 according toa first embodiment of the present invention. The laser diode module 40includes a base 41 having a first vertical portion 43c to which a laserdiode 42 is fixed. Further, the base 41 has a lens holder mounting part43, which includes a horizontal lens holder mounting portion 43a and asecond vertical portion 43b. The surfaces of the portions 43a and 43bare high-precision flat surfaces.

A lens holder 44 is of a substantially L-shape, and has a verticalportion 44a and a horizontal portion 44b. A lens 45 is fixed to thevertical portion 44a. A through female screw 46 is vertically formed atan end part of the horizontal portion 44b of the lens holder 44. Anadjustment male screw 47 for pivoting the hens holder 44 engages thefemale screw 46. An end portion of the adjustment male screw 47 canproject from the lower surface of the horizontal portion 44b of the lensholder 44.

A hole 48 that is long (i.e., elongated) the horizontal direction isformed in a vertical wall 41a of the base 41. A male screw 49 isinserted into the long hole 48 and is engaged with a female screw 50formed in a root portion at which the vertical portion 44a of the lensholder 44 and the horizontal portion 44b thereof are connected to eachother.

A leaf spring 51 presses the lens holder 44 against the lens holdermounting portion 43a of the lens holder 43.

An adjustment operation of the lens holder 44 is performed as follows.As shown in FIG. 6A, an optical bench 60 and a beam spot measuringinstrument 61 are used to perform the adjustment operation. At the firststep of the adjustment operation, the base 41 and the measuringinstrument 61 are placed on the optical bench 60 so that the distancebetween the laser diode 42 and the measuring instrument 61 is equal to apredetermined distance L.

At the second step of the adjustment operation, the horizontal-directionfocal point is adjusted as follows. The male screw 49 is turned (loosed)in a state in which the screw 47 does not project from the lower surfaceof the horizontal portion 44b of the lens holder 44. In other words, themale screw 49 is turned in a state in which the lens 45 is not tilt. Anoutput signal of the measuring instrument 61 is monitored while the lensholder 44 is made to slide on the lens holder mounting portion 43a in adirection indicated by a two-headed arrow A, as shown in FIG. 6A. Inthis manner, the position of the lens holder 44, at which a minimum beamspot size can be obtained, is identified. Therefore, the screw 49 issecured so that the lens holder 44 is provisionally fixed to the base41.

At the third step of the adjustment operation, the vertical-directionfocal point is adjusted as follows. The measuring instrument 61 is movedin a direction indicated by a single-headed arrow B, as shown in FIG.6A. Thereafter, the screw 47 is turned so that it projects downwardlyfrom the horizontal portion 44b of the lens holder 44. Hence, the screw47 presses downwardly on the lens holder mounting portion 43a, so thatthe lens holder 44 is turned (i.e., rotated) as indicated by an arrow Cshown in FIG. 6A. Hence, an angle θ between the vertical direction andthe vertical surface of the vertical portion 44a of the lens holder 44is formed. That is, the lens 45 is tilted by the angle θ in thecounterclockwise direction. It will be noted that the lens 45 is tiltedby tilting the lens holder 44 in the above-mentioned manner and hence nostress is exerted on the lens 45. The screw 47 is turned in order todetermine a tilted position of the lens holder 44 at which a minimumbeam spot size can be obtained. Then, the screw 49 is secured to fix thelens holder 44 to the base 41. When the third step of the adjustmentoperation is completed, the adjustment operation is completed.

As shown in FIG. 7A, the lens holder 44 has a chamfered corner 55. Atthe third step of the adjustment operation, the lens holder 44 is causedto pivot about an end 56 of the chamfered corner 55 in the directionindicated by the arrow C. The chamfered corner 55 is formed so that theend 56 is located just below the female screw 50. If the chamferedportion 55 is not formed, as shown in FIG. 7B, the position of thefemale screw 50 will greatly move in the vertical direction, and thepossible tilt angle θ will be limited to a narrow range due to therelation with the long hole 48. On the other hand, the chamfered corner55 causes the female screw 50 to be moved, as shown in FIG. 7A. It willbe seen from FIG. 7A that the position of the female screw 50 does notgreatly move in the vertical direction. With the above structure, it ispossible to cause the lens holder 44 to pivot about the end 56 up toapproximately 10° and to facilitate the adjustment of thevertical-direction focal point.

The leaf spring 51 presses the lens holder 44 against the lens holdermounting surface 43a. Hence, the lens holder 44 can be made to pivotabout the end 56 in the state where the end 56 is in contact with thelens holder mounting surface 43a of the base 41.

Alternatively, as shown in FIG. 8, it is possible to provide theadjustment screw 47 so that it engages a female screw 46a formed in thebase 41 and can project upwardly from the lens holder mounting surface43a of the base 41.

A description will now be given, with reference to FIGS. 9 and 10, of alaser diode module 40A according to a second embodiment of the presentinvention. In FIGS. 9 and 10, parts that are the same as those shown inthe previously described figures are given the same reference numbers.

The laser diode module 40A shown in FIGS. 9 and 10 has a base 41A havinga hole 71 which is formed in the vertical portion 41a of the base 41Aand is long (i.e., elongated) in the horizontal direction A. The lensholder 44 is rotatable in the direction indicated by the arrow C (FIG.10). A laser diode holder 70 is provided so that it can slide on thelens holder mounting surface 43a in the direction A (FIG. 9). It will benoted that the base 41A shown in FIGS. 9 and 10 does not have thevertical portion 43c of the base 41 shown in FIGS. 6A through 6C. Thelaser diode holder 70 can be fixed at a desired position by means of amale screw 72, which is inserted into the long hole 71 and is engagedwith a female screw formed in the laser diode holder 70.

The horizontal-direction focal point can be adjusted so that the laserdiode holder 70 is moved in the direction A. The vertical-directionfocal point can be adjusted by means of the screw 47 in the same manneras that in the first embodiment of the present invention.

A description will now be given, with reference to FIGS. 11A, 11B and11C, of a laser diode module 40B according to a third embodiment of thepresent invention. In FIGS. 11A through 11C, parts that are the same asthose shown in the previously described figures are given the samereference numbers.

A lens holder 44A, to be used instead of the aforementioned lens holder44, has a first vertical plate portion 81a and a second vertical portion81b. The lens holder 44A is an integrally formed member and the portions81a and 81b thereof are integrally formed and are opposite to each othervia a slit 80. The lens is fixed to the first vertical plate portion81a. The second vertical portion 81b has a through hole 80b extending inthe horizontal direction and allows the laser beam, via the lens 45, topass through the through hole 80b. A through female screw 84 is formedin the vertical portion 81b and is located above the through hole 80b. Amale screw 82, which engages the female screw 84, passes through theslit 80 and can come in contact with an upper portion of the verticalplate portion 81a. By turning the male screw 82, it gradually pressesthe vertical plate portion 81a, which is gradually bent and tilted, sothat the lens 45 is tilted by the angle θ. The slit 80 makes thevertical plate portion 81a flexible. In this manner, thevertical-direction focal point can be adjusted.

The horizontal-direction focal point can be adjusted in the same manneras that of the first embodiment of the present invention. That is, thelens holder 44A is slidable on the lens holder mounting surface 43a, andis fixed at a position where a minimum beam spot size can be obtained.

FIG. 12 is a diagram of a first variation 44B of the lens holder 44Aused in the third embodiment of the present invention. In FIG. 12, partsthat are the same as those shown in the previously described figures aregiven the same reference numbers. A groove 90 is formed in an outer rootportion of the vertical plate portion 81a. The groove 90 facilitate thedegree of flexibility of the vertical plate portion 81a.

FIG. 13 is a diagram of a second variation 44C of the lens holder 44Aused in the third embodiment of the present invention. In FIG. 13, partsthat are the same as those shown in the previously described figures aregiven the same reference numbers. The vertical portion 81b has ahorizontal projection 81b' located above the slit 80. A male screw 91vertically penetrates the horizontal portion 81b' and projectstherefrom. A female screw 91 engaging the male screw 91 is formed in thehorizontal projection 81b'. A wedge 92 is depressed by the male screw91, so that the wedge 92 is forced to be inserted into the slit 80. Theadjustment operation can be performed from the upper side of the laserdiode module without interrupting the laser beam emitted via the lens45.

FIG. 14 is a diagram of a third variation 44D of the lens holder 44Aused in the third embodiment of the present invention. In FIG. 14, partsthat are the same as those shown in the previously described figures aregiven the same reference numbers. A rod 93 having an oval cross-sectionis rotatably provided in the slit 80. By rotating the rod 93, thevertical plate portion 81a is bent, so that the lens 45 is tilted.

A description will now be given, with reference to FIGS. 15A, 15B and15C, of a laser diode module 40C according to a fourth embodiment of thepresent invention. In FIGS. 15A through 15C, parts that are the same asthose shown in the previously described figures are given the samereference numbers.

A lens holder 44B-1 includes the vertical projections 81a and 81b. Asloped portion 95 is formed on a corner of the vertical portion 81b. Aleaf spring 96 having an end embedded in the vertical portion 41b of thebase 41 engages the sloped portion 95 of the vertical portion 81b. Theleaf spring 96 urges the lens holder 44B-1 in a direction indicated byan arrow 97 shown in FIG. 15b. Hence, the lens holder 44B-1 is pressedagainst the lens holder mounting surface 43a and the vertical surface43b. After the positioning of the lens holder 44B-1 is completed, thelens holder 44B-1 can be fastened to the base 41 by means of an adhesiveor the like.

FIGS. 16A and 16B are diagrams of a laser diode module 40D according toa fifth embodiment of the present invention. In FIGS. 16A and 16B, partsthat are the same as those shown in the previously described figures aregiven the same reference numbers. A base 41B has a first vertical plateportion 101a and a second vertical portion 101b, these portions beingspaced apart from each other via a slit 100. The lens 45 is fixed to thevertical portion 101a. A male screw 102 engages a female screw formed inthe vertical portion 101b and projects therefrom. A through hole 103 isformed in the vertical portion 101b so that the laser beam passingthrough the lens 45 is allowed to pass. The screw 102 comes into contactwith an upper portion of the vertical portion 101a. By turning the screw102, the vertical portion 101a is bent and tilted, so that the lens 45can be tilted. The laser diode 42 is held by the laser diode holder 70,also used in the second embodiment of the present invention. Since thescrew 102 for the adjustment is provided in the base 41B fixed to theoptical bench, it is easy to operate the screw 102.

A description will now be given, with reference to FIGS. 17A, 17B and17C, of a laser diode module 40E according to a sixth embodiment of thepresent invention. The laser diode module 40E includes a base 111 havinga first vertical portion 111a, a second vertical portion 111b, and aholder mounting surface 111c. The first and second vertical portions111a and 111b are provided so that these portions form a right angle.The laser diode 42 is fixed to the second vertical portion 111b.

A holder 114 is mounted on the holder mounting surface 111c, and isslidable thereon. A leaf spring 113 fixes the holder 114 on the holdermounting surface 111c in a state in which the holder 114 is in contactwith the first vertical portion 111a of the base 111. One end of theleaf spring 113 is embedded in the first vertical portion 111a, and theother end engages an edge of the holder 114.

The holder 114 has a large cylindrical through hole 117, and two smallcylindrical holes 115 and 116. The holes 115 and 116 are located onrespective sides of the through hole 117 and are connected to thethrough hole 117. The laser beam emitted from the laser diode 42 entersinto the hole 116. The through hole 117 accommodates a lens holder 118having a cylindrical shape and almost the same diameter as that of theholder 114. The lens holder 118 has a through hole 120, which isintegrated with the holes 115 and 116 when the lens holder 118 isinserted into the holder 114 and placed in a position. The lens 45 islocated in the through hole 120 of the lens holder 118. The laser beamfrom the hole 116 passes through the lens 45 and is emitted through thehole 115. A straight groove 119 is formed on a front surface of the lensholder 118. By turning the lens holder 118, when accommodated in theholder 114, by means of an instrument engaged with the groove 119, it ispossible to tilt the lens 45 with respect to the laser beam emitted fromthe laser diode 42. Thereby, the vertical-direction focal point can beadjusted. The horizontal-direction focal point can be adjusted by movingthe holder 114 in the direction A.

A description will now be given, with reference to FIGS. 18A, 18B and18C, of a first variation 40F of the laser diode module 40E according tothe sixth embodiment of the present invention. In FIGS. 18A through 18C,parts that are the same as those shown in FIGS. 17A through 17C aregiven the same reference numbers.

The laser diode module 40F shown in FIGS. 18A through 18C has a leafspring 126 fastened to the holder 114 by means of a male screw 127. Theleaf spring 126 presses the lens holder 118 against the first verticalportion 111a of the base 111. Thereby, a deviation of the lens holder118 and the lens 45 in the direction perpendicular to the optical axisof the laser diode 42 can be prevented.

FIGS. 19A, 19B and 19C illustrate a second variation 40G of the laserdiode module 40E according to the sixth embodiment of the presentinvention. In FIGS. 19A through 19C, parts that are the same as thoseshown in the previously described figures are given the same referencenumbers.

The laser diode module 40G has a holder 114A having a through hole 117Aand the aforementioned holes 115 and 116. The lens holder 118 isinserted into the through hole 117A from the side of the holder 114Awhich is to come into contact with the first vertical portion 111a ofthe base 111. The diameter of the through hole 117A on the outsidethereof is less than the diameter of the lens holder 118. Hence, acircular edge portion of the lens holder 118 comes into contact with aninner wall of the through hole 117A of the holder 114A. In the state inwhich the holder 114A, with the lens holder 118 inserted therein, isplaced on the holder mounting surface 111c as shown in FIG. 19C, theleaf spring 113 presses the holder 114A against the first verticalportion 111a of the base 111 in such a state in which an end surface ofthe lens holder 118 opposite to the groove is in pressure contact withthe first vertical portion 111a of the base 111. Hence, it is possibleto deviate the lens holder 118 and the lens 45 from the predeterminedposition at which the optical axis of the laser diode 42 matches theoptical axis of the lens 45. The vertical-direction focal point can beadjusted by turning the lens holder 118 by means of an instrument.

A description will now be given, with reference to FIGS. 20A, 20B and20C, of a third variation 40H of the laser diode module 40E according tothe sixth embodiment of the present invention. FIGS. 20A, 20B and 20C,parts that are the same as those shown in the previously describedfigures are given the same reference numbers.

The laser diode module 40H shown in FIGS. 20A, 20B and 20C has a base131 having a hole 136 into which the lens holder 118 is inserted. A hole132 is joined to the hole 120 of the lens holder 118 when the lensholder 118 is inserted into the hole 138 and placed in a position. Asshown in FIG. 20A, a hole 133 is formed in the base 131 so that itreceives the laser beam emitted from the laser diode 42. The base 131has a laser diode holder accommodating space defined by a verticalportion 131a and a laser diode holder mounting surface 131b. Ablock-shaped laser diode holder 141, which is slidable on the mountingsurface 131b in the direction A, holds the laser diode 42. A leaf spring135, having an end embedded in the vertical portion 131a of the base131, engages an edge of the holder 141 and presses it against thevertical portion 131a. The horizontal-direction focal point can beadjusted by moving the laser diode holder 141 in the direction A. Thevertical-distance focal point can be adjusted by turning the lens holder118.

The present invention is not limited to the specifically describedembodiments and variations, and other variations and modifications maybe made without departing from the scope of the present invention.

What is claimed is:
 1. A laser diode module comprising:a laser diodeemitting a laser beam along an optical axis; a base which holds thelaser diode and has a mounting surface parallel to the optical axis ofthe laser diode; a lens for collimating the laser beam and having a lensaxis; a lens holder slidably mounted on the mounting surface of the baseand which holds the lens with the lens axis thereof alignedsubstantially with the optical axis, the lens, further, having atransverse axis passing through the center of the lens, transverse toand forming an intersection with the optical axis, the optical andtransverse axes defining a first reference plane, a second transverseaxis, transverse to the reference plane, passing through theintersection; a mechanism mounted on the base and which selectivelytilts the lens holder with respect to the mounting surface of the basethereby to selectively adjust the tilt angle of the lens; and said lensbeing selectively tilted about the first transverse axis to a selectedtilt angle, relative to the second transverse axis, at which a minimumbeam spot of the laser beam, at a focus position along the optical axis,is achieved at the focus position of the beam spot in both first andsecond directions, each thereof perpendicular to the optical axis andrespectively parallel to the first and second transverse axes.
 2. Thelaser diode module as claimed in claim 1, wherein said mechanismcomprises:a first screw rotatably received in the base and adjustable toan engaging position for engagingly holding the lens holder at a desiredposition thereof, as mounted on the mounting surface of the base; and asecond screw penetrating the lens holder and having an end whichprojects from the lens holder into contact with the mounting surface ofthe base.
 3. The laser diode module as claimed in claim 1, wherein saidmechanism comprises:a first screw rotatably adjustable to an engagingposition for engagingly holding the lens holder at a desired positionthereof, as mounted on the mounting surface of the base; and a secondscrew penetrating the base and having an end which projects from themounting surface of the base and comes into contact with the lensholder.
 4. The laser diode module as claimed in claim 1, furthercomprising a leaf spring supported by the base and resiliently engagedwith the lens holder for pressing the lens holder against the base. 5.The laser diode module as claimed in claim 1, wherein said base has astationary portion holding the laser diode at a fixed position, relativeto the mounting surface of the base, for emitting the laser beam alongthe optical axis to the lens.
 6. The laser diode module as claimed inclaim 2, wherein:the base has a threaded hole into which the first screwis inserted and received; and the threaded hole has a sufficient lengthto move the lens holder on the mounting surface of the base.
 7. Thelaser diode module as claimed in claim 1, wherein:the laser diodefurther comprises a laser diode holder that holds the laser diode and isslidably mounted on the mounting surface of the base for adjusting theposition thereof along the optical axis.
 8. The laser diode module asclaimed in claim 1, wherein:the lens holder further comprises a firstportion holding the lens and a second portion extending transversely tothe optical axis and spaced from the first portion by a slit; and thelens holder further comprises a screw passing in a directionsubstantially parallel to the optical axis and through a threadedaperture in the second portion and the slit and coming into contact withthe spaced, first portion and applying an adjustable force against thespaced, first portion when turned, thereby to adjust the tilt angle ofthe lens.
 9. The laser diode module as claimed in claim 8, wherein:thelens holder further comprises a base portion extending transversely toand integrally interconnecting the first and second portions; and thefirst portion of the lens holder has a groove therein at theinterconnection thereof with the base portion, facilitating bending ofthe first portion relatively to the base and second portions, relativelyto both the base portion and the spaced, second portion, by turning thescrew.
 10. The laser diode module as claimed in claim 1, furthercomprising:a base which holds the laser diode; a lens holder having afirst portion and a second portion opposite to the first portion via aslit, the second portion having a projection located above the slit; awedge engaging the slit; and a screw passing through the projection ofthe second portion and coming into contact with the wedge, wherein:thefirst portion of the lens holder holds the lens; and the first portionof the lens holder is bent by turning the screw so that a tilt angle ofthe lens with respect to the optical axis is propagated can be adjusted.11. The laser diode module as claimed in claim 1, further comprising:abase which holds the laser diode; a lens holder having a first portionand a second portion opposite to the first portion via a slit; and a rodprovided in the slit and coming into contact with the first and secondportions, said rod having an oval cross-section, wherein:the firstportion of the lens holder holds the lens; and the first portion of thelens holder is bent by turning the rod so that a tilt angle of the lenswith respect to the optical axis along which the laser beam ispropagated can be adjusted.
 12. The laser diode module as claimed inclaim 8, further comprising a leaf spring supported by the base andengaged with the lens holder,said leaf spring pressing the lens holderagainst the base.
 13. The laser diode module as claimed in claim 12,wherein:the base comprises a vertical portion; the lens holder has aslope portion; and the leaf spring has a bent portion engaging with theslope portion of the lens so that the lens holder is pressed against thevertical portion of the lens holder and the mounting surface thereof.14. The laser diode module as claimed in claim 1, further comprising:abase which holds the lens so that a tilt angle of the lens with respectto the optical axis can be adjusted and which is mounted on the base,said base having a mounting surface; and a laser diode holder whichholds the laser diode and is slidably mounted on the mounting surface ofthe base.
 15. The laser diode module as claimed in claim 14, wherein:thebase has a first portion and a second portion opposite to the firstportion via a slit; the laser diode module comprises a screw passingthrough the second portion and coming into contact with the firstportion via the slit:the first portion of the base holds the lens; andthe first portion of the base is bent by turning the screw so that atilt angle of the lens with respect to the optical axis along which thelaser beam is propagated can be adjusted.
 16. The laser diode module asclaimed in claim 1, further comprising:a base holding the laser diodeand having a mounting surface; a first lens holder holding the lens; anda second holder slidably mounted on the mounting surface of the base,wherein:the first lens holder has a first through hole in which the lensis placed; the second holder has a second hole into which the first lensholder is inserted, and two third holes joined to the first through holeand formed on respective sides of the first through hole; and the laserbeam emitted from the laser diode is propagated through one of the twothird holes, a part of the second hole, the lens, a remaining part ofthe second hole, and the other one of the two third holes.
 17. The laserdiode module as claimed in claim 16, wherein:the first lens holder has acylindrical shape; the second hole has a cylindrical shape correspondingto the cylindrical shape of the first lens holder; and the first lensholder has a groove into which an instrument is to be inserted byturning the first lens holder.
 18. The laser diode module as claimed inclaim 16, further comprising a leaf spring having a first end fixed tothe base, and a second end engaged with the second holder, so that thesecond holder is pressed against the base.
 19. The laser diode module asclaimed in claim 16, further comprising a leaf spring having a first endfixed to the second holder, and a second end engages with the first lensholder, so that the first lens holder is pressed against the base. 20.The laser diode module as claimed in claim 16, wherein one end of thefirst through hole has a first diameter less than a second diameter ofthe first lens holder, so that the first lens holder comes into contactwith an inner wall of the first through hole defining the firstdiameter.
 21. The laser diode module as claimed in claim 1, furthercomprising:a base having a mounting surface, a first hole, and twosecond holes joined to the first hole and formed on respective sides ofthe first through hole; a lens holder which is inserted into the firsthole; and a laser diode holder which holds the laser diode and isslidably mounted on the mounting surface of the base, wherein:the lensholder has a third hole in which the lens is placed; and the laser beamemitted from the laser diode is propagated through one of the two secondholes, a part of the third hole, the lens, a remaining part of the thirdhole, and the other one of the two second holes.
 22. The laser diodemodule as claimed in claim 21, wherein:the lens holder has a cylindricalshape; the first hole has a cylindrical shape corresponding to thecylindrical shape of the first lens holder; and the lens holder has agroove into which an instrument is to be inserted by turning the lensholder.
 23. A laser diode module comprising:a base defining a baseoptical axis and first and second mounting surfaces displaced along thebase optical axis by a selected axial distance; a laser diode supportedon the first mounting surface and emitting a laser beam along the baseoptical axis; a holder supported on the second mounting surface andholding a lens, having a lens optical axis, centered on the base opticalaxis and displaced from the laser diode by a selected axial distance,the holder providing for selective tilting of the lens and therebyselectively varying a tilt angle of the lens optical axis relatively tothe base optical axis; and a mechanism maintaining the lens at aselected angle which, with the lens at the selected axial distance fromthe laser diode, produces a minimum beam spot of the laser beam, at afocus position along the base optical axis, in both of first and secondmutually perpendicular directions, each direction being perpendicular tothe base optical axis.
 24. A laser diode module as claimed in claim 23,wherein:the base further comprises an upright base portion having thefirst mounting surface therein, the second mounting surface comprising aplanar surface extending from the upright base portion, parallel to andspaced from the base optical axis; the holder has a lower planar surfacereceived on and selectively tilted with respect to the planar, secondmounting surface for selective tilting of the lens; and the mechanismselectively tilts the holder, and thereby the lens, relatively to theplanar mounting surface thereby to select and to maintain the selectedtilt angle of the lens.
 25. The laser diode module as claimed in claim23, wherein:the second mounting surface of the base is a planar mountingsurface extending parallel to and spaced from the base optical axis; theholder further comprises:a bottom portion having a planar bottom surfacereceived on the second, planar mounting surface of the base, first andsecond end portions extending upwardly from the bottom portion of theholder, the first portion being rigidly connected to the bottom portionand the second portion being resiliently connected to the bottom portionand spaced via a slit from the first portion, the second portion holdingthe lens therein and the first portion having an opening therein alignedwith the optical axis and through which the laser beam passes; and themechanism selectively tilts the second portion of the holder to aselected, angularly displaced position relatively to the first portionof the holder and with respect to the mounting surface of the base andthe optical axis thereby to select and maintain the selected tilt angleof the lens.
 26. The laser diode module as claimed in claim 25,wherein:said base further comprises an upright wall extending parallelto the base optical axis and transversely to the second, planar mountingsurface and having an elongated slot therein, extending parallel to thebase optical axis; and said mechanism further comprises:a first screwextending through the elongated slot and engaging the holder andadjustable by rotation relative to the base and the holder for releasingthe holder to permit selective tilting of the holder and the lens,relatively to the second, planar mounting surface of the base, and toengage the holder to the base with the holder displaced from the laserdiode by the selected axial distance, and a second screw extending inthreaded engagement through the holder and having an end which projectsfrom the planar bottom surface of the holder and into contact with theplanar, second mounting surface of the base and adjustable by selectiverotation thereof relatively to the holder so as to select and maintainthe selected tilt angle of the lens.
 27. The laser diode module asclaimed in claim 25, wherein:said base further comprises an upright wallextending parallel to the base optical axis and transversely to thesecond, planar mounting surface and having an elongated slot therein,extending parallel to the base optical axis; and said mechanism furthercomprises:a first screw extending through the elongated slot andengaging the holder and adjustable by rotation relative to the base andthe holder for releasing the holder to permit selective tilting of theholder and the lens, relatively to the second, planar mounting surfaceof the base, and to engage the holder to the base with the holderdisplaced from the laser diode by the selected axial distance, and asecond screw threadingly received in and extending through the base andhaving an end which projects above the planar, second mounting surfaceof the base and into contact with the planar bottom surface of theholder and adjustable by selective rotation thereof, relatively to thebase, to vary the projection of the end thereof relatively to thesecond, planar mounting surface of the base and thereby to selectivelytilt the holder and thereby the lens so as to select and to maintain theselected tilt angle of the lens.
 28. The laser diode module as claimedin claim 25, further comprising a resilient element having a first endsecured to the base and a second end engaging the holder and resilientlypressing the holder against the base.
 29. The laser diode module asclaimed in claim 26, wherein:the base has a hole through which the firstscrew is inserted and which is of sufficient length, parallel to thebase optical axis, to move the holder along the upper planar mountingsurface of the base.
 30. The laser diode module as claimed in claim 23,wherein:the holder further comprises a base portion having a bottomplanar surface received on the second mounting surface and having firstand second portions extending upwardly therefrom in spaced relationshipwith a slit therebetween, the first portion being rigidly connected withthe base portion and the second portion being flexibly connected withthe base portion, the first portion defining a through hole aligned withthe optical axis and through which the laser beam passes and the secondportion holding the lens therein; and the mechanism further comprises ascrew threadingly engaged in and passing through the first portion andthe slit and coming into contact with the second portion, the screwbeing adjustable by selective rotation thereof, relatively to the firstportion, to angularly and resiliently deflect the second portionrelative to the first portion so as to select and to maintain the lensat the selected tilt angle.
 31. The laser diode module as claimed inclaim 30, wherein the second portion of the holder has a groove formedtherein, transverse to the optical axis and facilitating deflecting ofthe second portion.
 32. The laser diode module as claimed in claim 30,further comprising a leaf spring having a first end secured to the baseand a second end engaging the lens holder and resiliently pressing thelens holder against the base.
 33. The laser diode module as claimed inclaim 32, wherein the holder further comprises:a first holder portionhaving a first through hole, in which the lens is placed, for holdingthe lens; and a second holder portion mounted on the second mountingsurface of the base and having a second through hole into which thefirst holder portion is inserted, and third and fourth through holesjoined to the first through hole and formed on respective, opposingsides of the first through hole, andthe first through fourth throughholes are aligned along the base optical axis.
 34. The laser diodemodule as claimed in claim 33, wherein:the first holder portion has acylindrical outer shape; the second holder portion has an innercylindrical opening corresponding to the cylindrical outer shape of thefirst holder portion and receiving the first holder portion therein, thefirst holder portion being rotatable relatively to the second holderportion for selectively tilting the lens to the selected tilt angle. 35.The laser diode module as claimed in claim 23, wherein the base furthercomprises an upright portion, transverse to the base optical axis, andthe first mounting surface is defined by an opening in the uprightportion of the base in which the laser diode is received and supported.36. The laser diode module as claimed in claim 23, wherein the basefurther comprises an upright portion, transverse to the base opticalaxis, and the second mounting surface is defined by an opening in theupright portion of the base in which the holder is received andsupported.
 37. A laser diode module comprising:a base defining an upper,planar mounting surface; a lens supported on the base in alignment withan optical axis parallel to the upper, planar mounting surface; a laserdiode emitting a laser beam along the optical axis; a holder having alower planar mounting surface supported on, and moveable in slidingrelationship relatively to, the upper planar mounting surface of thebase to a selected holder position and which holds a selected one of thelaser diode and the lens at a selected position relatively to, anddisplaced by a selected distance from, the other of the laser diode andthe lens, along the optical axis; and a mechanism interconnecting thebase and the holder and maintaining the lens holder and thereby the lensat a selected tilt angle with respect to the upper planar mountingsurface of the base and at the selected distance along the base opticalaxis, between the lens and the laser diode, minimizing the beam size inone of horizontal and vertical directions relative to the optical axis.38. A laser diode module as recited in claim 37, wherein:the lensreceives the laser beam and converges the laser beam passingtherethrough so as to define a vertical beam waist at a correspondingfirst axial position along the optical axis and a horizontal beam waistat a corresponding second axial position along the optical axis; theselected distance along the base optical axis minimizes the size of thehorizontal beam waist at the second axial position; and the selectedtilt angle of the lens produces a minimum vertical beam waist, andthereby a minimum beam size, at the second axial position.